Usually that means your starter is on the way out. What year is the truck? Mileage?
My vette did that for a couple times before the starter completely decided to stop. And that was like in 2008. Not bad, that starter got 13 years of life.
I ended up spending 90 bucks to have it completely rebuilt.
Disconnect the battery and pull the starter yourself and take it to a shop that rebuilds starters. Save yourself a couple hundred bucks.
Also, if you can't start it at all, try tapping the starter with a hammer and give it another go.